1. Technical Field
The present invention relates in general to improvements in data transmission systems and in particular to enhanced methods and systems for data transmission in a cellular telephone system. Still more particularly, the present invention relates to an improved method and system for transmitting data packets within alternate adjacent buffer voice channels in a cellular telephone system.
2. Description of the Related Art
Data communication between modern computer devices is typically accomplished utilizing a modulator/demodulator or so-called "modem" which is utilized to convert digital signals within a data processing system to analog signals for transmittal over existing communication links. Additionally, such devices convert received analog signals to digital signals for utilization by a data processing system. In the past most distributed computer networks have been coupled together utilizing existing telephone land line systems, or specialized wiring; however, modern distributed data processing systems often utilize more sophisticated means of communication.
For example, the decreasing cost of cellular communication equipment has resulted in the utilization of that technology to couple together computers without the necessity of access to a telephone line outlet. This particular technology is particularly effective in combination with small portable battery powered laptop or notebook computers in which the necessary modem and cellular communication circuitry are miniaturized and provided in an integral fashion within the computer itself. Thus, an operator utilizing such a computer may initiate communications and transfer data between his or her computer and a distributed data processing system without the necessity of access to either telephone lines or power lines. Examples of such portable computers include the International Business Machines Corporation L40SX and the Model No. 9075 PCradio which may be utilized for wireless communication by attaching a radio device. Radio devices such as cellular telephone transceivers or ARDIS radio devices may be utilized.
Mobile data terminals which comprise battery powered data processing systems with cellular transceiver networks may be utilized to provide packet-switched access to services on remote hosts or other mobile data terminals by transmitting data via a cellular telephone system. Such systems typically support both voice and other analog traffic and the operation of such systems may be continued at full capacity, without awareness or interaction, with a data transmission system. Each mobile data terminal in such a system generally consists of an application component and a communications component, together referred to as a "subscriber unit." Data is accepted and forwarded to and from subscriber units by a Mobile Data Base System (MDBS) which manages the allocation of channels within a cellular telephone system.
In known prior art data transmission systems which utilize a cellular telephone system, communication between a subscriber unit and the MDBS takes place over a pair of channels. Subscriber units receive data from the MDBS over a "forward channel" and transmit data to the MDBS over a "reverse channel." The two channels utilized are related as set forth in the EIA/TIA-553 standard. An MDBS may maintain several forward channels simultaneously for communication with different sets of subscriber units and a given reverse channel may be multiplexed among subscriber units tuned to the corresponding forward channel. When a channel pair which is utilized for data transmission is reassigned to a new analog cellular circuit, the MDBS and subscriber units switch to another free channel and continue to operate in a procedure known as "channel hopping."
While such systems permit the transfer of data utilizing analog voice channels within a cellular telephone system, the increased utilization of cellular telephone systems for data transmission has resulted in an increased demand on such systems. As those skilled in the art will appreciate in such systems assigned voice channels are utilized for communication; however, each assigned voice channel is surrounded by vacant adjacent channels which are utilized to minimize interference between adjacent channels. It has recently been proposed that these vacant adjacent voice channels be utilized for data transmission by utilizing a very narrow band modulated carrier within one of these adjacent channels. By running such a data transmission at very low speeds and signal strength, the interference with adjacent assigned voice channels may be minimized; however, the resultant data transmission rates are generally not sufficient for modern data transmission systems.
It should therefore be apparent that a need exists for a method and system which will enhance the efficiency of data transmission within a cellular telephone system.